This invention relates to the removal of a metal oxide coating from a superalloy article.
In an aircraft gas turbine (jet) engine, air is drawn into the front of the engine and compressed by an axial-flow compressor. The axial-flow compressor includes a number of compressor stages. Each compressor stage has a plurality of compressor blades mounted to a compressor disk, which in turn is mounted to a rotating shaft.
In many early versions of gas turbine engines, the compressor blades were made of an uncoated metal. As the technology of gas turbine engines has advanced and the temperatures of operation have increased, it has become necessary to coat the compressor blades to inhibit oxidation of the metal during extended service. The coatings need not be as protective and as resistant to the effects of the combustion gas at high temperatures as the environmental coatings and thermal barrier coatings used on the turbine blades, but they must provide oxidation protection at intermediate temperatures. Chromium and aluminum oxide coatings cured in the presence of an inorganic binder have been selected for use to coat the compressor blades of the high pressure compressor stages of some engines.
The application of metal oxide coatings onto compressor blades, high pressure turbine disks and seals, and other components of gas turbine engines should meet specific standards to ensure proper performance of the metal oxide coating on the component over and extended service life. When the application is not properly applied according to the specification, or a flaw in the application process occurs, the metal oxide coating is usually completely removed from article down to the base metal, before re-application of the oxide coating.
A chemical method is preferred for removing initially-applied oxide coatings from superalloy compressor blades, high pressure turbine disks and seals, other component of a gas turbine engine. The present invention provides an improved process for removing an oxide coating from a gas turbine engine component.